While, in a normal woven material, the weft threads generally cross the warp threads at an angle of 90 degrees, this relation tends to be frequently destroyed in the course of dying, treatment, and finishing of the woven material, and causes a distorted texture such as bending or slanting of the weft threads. This gives rise to such problems as a distortion in the dyed pattern or failure to hold the shape after sewing. In the past, it has been impossible to completely eliminate the occurrence of such distorted texture in spite of many different measures which have heretofore been proposed for this purpose. As a result, a variety of methods has been used to detect the bending of the weft threads in a woven material having a distorted texture and to correct the distorted texture mechanically.
Previously known methods for detecting the distorted texture of woven material are typically designed so that an image of the weft threads formed by the light transmitted through the woven material is detected.
A first known method comprises collimating the light from a light source with a projector lens and passing it through a moving woven material. The light is detected in a photoelectric transducer located behind a rectangular slit which is mechanically scanned and arranged so that the slit major axis extends substantially parallel to the weft threads of the woven material. Thus, a change in the intensity of the light incident on a photoelectric transducer is converted into an electric signal, is then amplified, and is shaped to generate a voltage proportional to the amplitude of the alternating voltage. The output voltage assumes a maximum value when the major axis direction of the slit aligns with the direction of the weft threads of the woven material. In other words, the direction of the slit which corresponds to the maximum output voltage represents the direction of the weft threads. As a result, if the slit is scanned mechanically over a suitable range of angles centering about an angle of 90 degrees with respect to the warp threads of the moving woven material, the slit angle at which the maximum output voltage for the scanning is produced will indicate the angle of the weft threads, thus making it possible to detect the presence of any distorted texture.
A second known method employs two units of the above-mentioned thread angle detector comprising a light source, a projector lens, a condensing lens, a slit and a photoelectric transducer. The detectors are symmetrically arranged side by side and at some angle with respect to the direction perpendicular to the warp threads of the woven material. Thus, since the difference between two output voltages is zero when the weft threads are perpendicular to the warp threads, when the voltage difference assumes a positive or negative value, variation in the angle of the weft threads is indicated.
While neither of these methods presents a problem in the case of a textile weave in which the image of the weft threads is relatively uncomplicated, they are disadvantageous in the case of a twill weave or satin weave because the image of the weft threads is difficult to distinguish. In such circumstances, a sufficient output voltage cannot be generated and, even if sufficient output voltage were obtained, it would (practically speaking) have no correlation with the direction of the weft threads, and this would make it impossible or difficult to detect the presence of a distorted texture. Another disadvantage of the first method is that, since the slit is scanned mechanically, it is impossible to increase the scanning speed. This results in a slow detection speed and a deteriorated response, thus making it disadvantageous to use the arrangement as a detecting means for an automatic distorted texture correcting apparatus.
The second method is also disadvantageous in that, even in the case of a plain weave in which detection is considered relatively easy, the proper detecting action cannot be ensured where there is a large difference between the preset angle of the slit and the angle of the weft threads, that is, when there exists a very large texture distortion.